Secondary metabolites as chemical signals for cellular differentiation

Genome mining and UHPLC-QTOF-MS/MS to identify the potential antimicrobial compounds and determine the specificity of biosynthetic gene clusters in Bacillus subtilis NCD-2

Background

Bacillus subtilis strain NCD-2 is an excellent biocontrol agent against plant soil-borne diseases and shows broad-spectrum antifungal activities. This study aimed to explore some secondary metabolite biosynthetic gene clusters and related antimicrobial compounds in strain NCD-2. An integrative approach combining genome mining and structural identification technologies using ultra-high-performance liquid chromatography coupled to quadrupole time-of-flight tandem mass spectrometry (UHPLC-MS/MS), was adopted to interpret the chemical origins of metabolites with significant biological activities.

Results

Genome mining revealed nine gene clusters encoding secondary metabolites with predicted functions, including fengycin, surfactin, bacillaene, subtilosin, bacillibactin, bacilysin and three unknown products. Fengycin, surfactin, bacillaene and bacillibactin were successfully detected from the fermentation broth of strain NCD-2 by UHPLC-QTOF-MS/MS. The biosynthetic gene clusters of bacillaene, subtilosin, bacillibactin, and bacilysin showed 100% amino acid sequence identities with those in B. velezensis strain FZB42, whereas the identities of the surfactin and fengycin gene clusters were only 83 and 92%, respectively. Further comparison revealed that strain NCD-2 had lost the fenC and fenD genes in the fengycin biosynthetic operon. The biosynthetic enzyme-related gene srfAB for surfactin was divided into two parts. Bioinformatics analysis suggested that FenE in strain NCD-2 had a similar function to FenE and FenC in strain FZB42, and that FenA in strain NCD-2 had a similar function to FenA and FenD in strain FZB42. Five different kinds of fengycins, with 26 homologs, and surfactin, with 4 homologs, were detected from strain NCD-2. To the best of our knowledge, this is the first report of a non-typical gene cluster related to fengycin synthesis.

Conclusions

Our study revealed a number of gene clusters encoding antimicrobial compounds in the genome of strain NCD-2, including a fengycin synthetic gene cluster that might be unique by using genome mining and UHPLC–QTOF–MS/MS. The production of fengycin, surfactin, bacillaene and bacillibactin might explain the biological activities of strain NCD-2.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-020-07160-2.

Protein tyrosine phosphorylation in streptomycetes

Using phosphotyrosine-specific antibodies, we demonstrate that in several Streptomyces spp. a variety of proteins are phosphorylated on tyrosine residues. Tyrosine phosphorylation was found in a number of Streptomyces species including Streptomyces lividans, Streptomyces hygroscopicus and Streptomyces lavendulae. Each species exhibited a unique pattern of protein tyrosine phosphorylation. Moreover, the patterns of tyrosine phosphorylation varied during the growth phase and were also influenced by culture conditions. We suggest that metabolic shifts during the complex growth cycle of these filamentous bacteria, and possibly secondary metabolic pathways, may be controlled by the action of protein tyrosine kinases and phosphatases, as has been demonstrated in signal transduction pathways in eukaryotic organisms.

Genetic regulation of secondary metabolic pathways in Streptomyces

Streptomyces species are (along with the fungi) the best-known antibiotic-producing organisms. Often, they make several different antibiotics. The biosynthesis of each antibiotic is encoded by a complex gene cluster that usually also contains regulatory and resistance genes. Typically, there may be more than one such pathway-specific regulatory gene per cluster. Both activator and repressor genes are known. Some of the regulatory genes for different pathways are related. In S. coelicolor, expression of several such biosynthetic gene clusters also depends on at least 11 globally acting genes, at least one of which is involved in the translation of a rare codon (UUA). A protein phosphorylation cascade also seems to be involved. Gene clusters closely similar to those for the biosynthesis of aromatic polyketide antibiotics determine spore pigment in some species. These genes show different regulation from antibiotic production genes. The evolution of gene clusters for polyketide antibiotics, and the possible adaptive benefits of secondary metabolism, are discussed.

rag genes: novel components of the RamR regulon that trigger morphological differentiation in Streptomyces coelicolor

The filamentous bacterium, Streptomyces coelicolor, undergoes a complex cycle of growth and development in which morphological differentiation coincides with the activation of the orphan response regulator RamR and the biosynthesis of a morphogenic peptide called SapB. SapB is a lantibiotic-like molecule derived from the product of the ramS gene that promotes formation of aerial hyphae by breaking the aqueous tension on the surface of the substrate mycelium. A ramR-disrupted mutant is delayed in aerial hyphae formation while constitutive overexpression of ramR accelerates aerial hyphae formation in the wild-type strain and restores SapB biosynthesis and aerial hyphae formation in all developmental mutants (bld) tested. Using DNA microarrays to globally identify S. coelicolor genes whose transcription was affected by ramR mutation or overexpression, we discovered a ramR-activated locus of contiguous cotranscribed developmental genes that modulate both aerial hyphae formation and sporulation. The genes of this cluster of ramR-activated genes (rag), which are chromosomally distant from previously known RamR-regulated genes, include: ragA (sco4075) and ragB (sco4074), which encode two subunits of an ABC transporter, ragK (sco4073), a putative histidine kinase, and ragR (sco4072), a ramR paralogue. Promoter mapping and protein-DNA binding experiments indicate that RamR activates ragABKR transcription directly, by binding to three sequence motifs in the ragABKR promoter region. A constructed ragABKR null mutant was able to synthesize SapB and erect aerial hyphae; however, these hyphae were unusually branched, reminiscent of substrate hyphae. Subsequent stages of differentiation, septation and sporogenesis were delayed. The role of ragABKR in aerial hyphae formation was shown both by epistasis (ragR-activated aerial hyphae formation in bld mutants) and extracellular complementation (ragR-induced synthesis of an activity allowing aerial hyphae formation in bld mutants) experiments. In conclusion, the ragABKR locus activates a SapB-independent developmental pathway that is involved in both aerial hyphae formation and sporulation, serving to integrate sequential morphogenic changes.

Aflatoxin biosynthesis gene clusters and flanking regions

AIMS

To compare the biosynthetic gene cluster sequences of the main aflatoxin (AF)-producing Aspergillus species.

METHODS AND RESULTS

Sequencing was on fosmid clones selected by homology to Aspergillus parasiticus sequence. Alignments revealed that gene order is conserved among AF gene clusters of Aspergillus nomius, A. parasiticus, two sclerotial morphotypes of Aspergillus flavus, and an unnamed Aspergillus sp. Phylogenetic relationships were established using the maximum likelihood method implemented in PAUP. Based on the Eurotiomycete/Sordariomycete divergence time, the A. flavus-type cluster has been maintained for at least 25 million years. Such conservation of the genes and gene order reflects strong selective constraints on rearrangement. Phylogenetic comparison of individual genes in the cluster indicated that ver-1, which has homology to a melanin biosynthesis gene, experienced selective forces distinct from the other pathway genes. Sequences upstream of the polyketide synthase-encoding gene vary among the species, but a four-gene sugar utilization cluster at the distal end is conserved, indicating a functional relationship between the two adjacent clusters.

CONCLUSIONS

The high conservation of cluster components needed for AF production suggests there is an adaptive value for AFs in character-shaping niches important to those taxa.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first comparison of the complete nucleotide sequences of gene clusters harbouring the AF biosynthesis genes of the main AF-producing species. Such a comparison will aid in understanding how AF biosynthesis is regulated in experimental and natural environments.

Molecular genetic analysis and regulation of aflatoxin biosynthesis

Aflatoxins, produced by some Aspergillus species, are toxic and extremely carcinogenic furanocoumarins. Recent investigations of the molecular mechanism of AFB biosynthesis showed that the genes required for biosynthesis are in a 70 kb gene cluster. They encode a DNA-binding protein functioning in aflatoxin pathway gene regulation, and other enzymes such as cytochrome p450-type monooxygenases, dehydrogenases, methyltransferases, and polyketide and fatty acid synthases. Information gained from these studies has led to a better understanding of aflatoxin biosynthesis by these fungi. The characterization of genes involved in aflatoxin formation affords the opportunity to examine the mechanism of molecular regulation of the aflatoxin biosynthetic pathway, particularly during the interaction between aflatoxin-producing fungi and plants.

Use of direct-infusion electrospray mass spectrometry to guide empirical development of improved conditions for expression of secondary metabolites from actinomycetes

A major barrier in the discovery of new secondary metabolites from microorganisms is the difficulty of distinguishing the minor fraction of productive cultures from the majority of unproductive cultures and growth conditions. In this study, a rapid, direct-infusion electrospray mass spectrometry (ES-MS) technique was used to identify chemical differences that occurred in the expression of secondary metabolites by 44 actinomycetes cultivated under six different fermentation conditions. Samples from actinomycete fermentations were prepared by solid-phase extraction, analyzed by ES-MS, and ranked according to a chemical productivity index based on the total number and relative intensity of ions present in each sample. The actinomycete cultures were tested for chemical productivity following treatments that included nutritional manipulations, autoregulator additions, and different agitation speeds and incubation temperatures. Evaluation of the ES-MS data from submerged and solid-state fermentations by paired t test analyses showed that solid-state growth significantly altered the chemical profiles of extracts from 75% of the actinomycetes evaluated. Parallel analysis of the same extracts by high-performance liquid chromatography-ES-MS-evaporative light scattering showed that the chemical differences detected by the ES-MS method were associated with growth condition-dependent changes in the yield of secondary metabolites. Our results indicate that the high-throughput ES-MS method is useful for identification of fermentation conditions that enhance expression of secondary metabolites from actinomycetes.

Effect of butyrolactone I on the producing fungus, Aspergillus terreus

Butyrolactone I [alpha-oxo-beta-(p-hydroxyphenyl)-gamma-(p-hydroxy-m-3, 3-dimethylallyl-benzyl)-gamma-methoxycarbonyl-gamma-butyrolactone] is produced as a secondary metabolite by Aspergillus terreus. Because small butyrolactone-containing molecules act as self-regulating factors in some bacteria, the effects of butyrolactone I on the producing organism were studied; specifically, changes in morphology, sporulation, and secondary metabolism were studied. Threefold or greater increases in hyphal branching (with concomitant decreases in the average hyphal growth unit), submerged sporulation, and secondary metabolism were observed when butyrolactone I was added to cultures of A. terreus. Among the secondary metabolites whose production was increased by this treatment was the therapeutically important compound lovastatin. These findings indicate that butyrolactone I induces morphological and sporulation changes in A. terreus and enhances secondary metabolite production in a manner similar to that previously reported for filamentous bacteria.

Aspergillus sporulation and mycotoxin production both require inactivation of the FadA G alpha protein-dependent signaling pathway

The filamentous fungus Aspergillus nidulans contains a cluster of 25 genes that encode enzymes required to synthesize a toxic and carcinogenic secondary metabolite called sterigmatocystin (ST), a precursor of the better known fungal toxin aflatoxin (AF). One ST Cluster (stc) gene, aflR, functions as a pathway-specific transcriptional regulator for activation of other genes in the ST pathway. However, the mechanisms controlling activation of aflR and synthesis of ST and AF are not understood. Here we show that one important level for control of stc gene expression requires genes that were first identified as early acting regulators of asexual sporulation. Specifically, we found that loss-of-function mutations in flbA, which encodes a RGS domain protein, or dominant activating mutations in fadA, which encodes the alpha subunit of a heterotrimeric G protein, block both ST production and asexual sporulation. Moreover, overexpression of flbA or dominant interfering fadA mutations cause precocious stc gene expression and ST accumulation, as well as unscheduled sporulation. The requirement for flbA in sporulation and ST production could be suppressed by loss-of-function fadA mutations. The ability of flbA to activate stc gene expression was dependent upon another early acting developmental regulator, fluG, and AflR, the stc gene-specific transcription factor. These results are consistent with a model in which both asexual sporulation and ST production require inactivation of proliferative growth through inhibition of FadA-dependent signaling. This regulatory mechanism is conserved in AF-producing fungi and could therefore provide a means of controlling AF contamination.

A physiological model for the control of erythromycin production in batch and cyclic fed batch culture

Reported differences in antibiotic production dynamics resulting from altering the growth-limiting nutrient (growth-dissociated production in carbon-limited culture and apparent growth-associated production in nitrogen-limited culture) are due to the different effects on growth kinetics. The substrate affinity for nitrate is significantly lower than that for glucose, resulting in nitrogen limitation effectively occurring throughout the culture. Glucose limitation occurs later in the culture, coinciding with the induction of antibiotic production. Induction occurs at the start of nitrogen-limited culture so that production appears to be growth-associated. Evidence that this hypothesis is consistent with production kinetics in cyclic fed batch culture was also obtained.

Bacterial avirulence genes

Although more than 30 bacterial avirulence genes have been cloned and characterized, the function of the gene products in the elictitation of resistance is unknown in all cases but one. The product of avrD from Pseudomonas syringae pv. glycinea likely functions indirectly to elicit resistance in soybean, that is, evidence suggests the gene product is an enzyme involved in elicitor production. In most if not all cases, bacterial avirulence gene function is dependent on interactions with the hypersensitive response and pathogenicity (hrp) genes. Many hrp genes are similar to genes involved in delivery of pathogenicity factors in mammalian bacterial pathogens. Thus, analogies between mammalian and plant pathogens may provide needed clues to elucidate how virulence gene products control induction of resistance.

Cloning and characterization of the A-factor receptor gene from Streptomyces griseus

A-factor (2-isocapryloyl-3R-hydroxymethyl-gamma-butyrolactone) and its specific receptor protein control streptomycin production, streptomycin resistance, and aerial mycelium formation in Streptomyces griseus. The A-factor receptor protein (ArpA) was purified from a cell lysate of S. griseus IFO 13350. The NH2-terminal amino acid sequences of ArpA and lysyl endopeptidase-generated fragments were determined for the purpose of preparing oligonucleotide primers for cloning arpA by the PCR method. The arpA gene cloned in this way directed the synthesis of a protein having A-factor-specific binding activity when expressed in Escherichia coli under the control of the T7 promoter. The arpA gene was thus concluded to encode a 276-amino-acid protein with a calculated molecular mass of 29.1 kDa, as determined by nucleotide sequencing. The A-factor-binding activity was observed with a homodimer of ArpA. The NH2-terminal portion of ArpA contained an alpha-helix-turn-alpha-helix DNA-binding motif that showed great similarity to those of many DNA-binding proteins, which suggests that it exerts its regulatory function for the various phenotypes by directly binding to a certain key gene(s). Although a mutant strain deficient in both the ArpA protein and A-factor production overproduces streptomycin and forms aerial mycelium and spores earlier than the wild-type strain because of repressor-like behavior of ArpA, introduction of arpA into this mutant abolished simultaneously its streptomycin production and aerial mycelium formation. All of these data are consistent with the idea that ArpA acts as a repressor-type regulator for secondary metabolite formation and morphogenesis during the early growth phase and A-factor at a certain critical intracellular concentration releases the derepression, thus leading to the onset of secondary metabolism and aerial mycelium formation. The presence of ArpA-like proteins among Streptomyces spp., as revealed by PCR, together with the presence of A-factor-like compounds, suggests that a hormonal control similar to the A-factor system exists in many species of this genus.

Signal transduction and secondary metabolism: prospects for controlling productivity

Evidence is accumulating that demonstrates the key roles played by diffusible molecules in regulating cellular differentiation, even among prokaryotic microorganisms. This is exemplified by A-factor and its analogues, which act as autoregulators for morphological differentiation and secondary metabolism in Streptomyces. The identification of a specific receptor for A-factor and an A-factor-controlled promoter sequence in S. griseus indicate the close similarity of this system to eukaryotic hormonal control. The involvement of prokaryotic homologues of the eukaryotic Ser/Thr-kinases in the regulation of differentiation processes seems to be another characteristic feature of this group of bacteria. Recent evidence for the presence of these molecular signalling systems in Streptomyces is reviewed, along with the inherent implications.

Microbial adaptation to a changeable environment: cell-cell interactions mediate physiological and genetic differentiation

Recent work by Magnuson, Solomon and Grossman(1) adds to a growing body of evidence indicating that microorganisms possess sophisticated signaling systems that enable them to sense and respond to environmental challenges. Typically, this response results in morphological, physiological and even genetic differentiation, paralleling that observed among higher organisms. These signaling systems may be interpreted as adaptations that maximize the reproductive potential of a population.

A-factor as a microbial hormone that controls cellular differentiation and secondary metabolism in Streptomyces griseus

A-factor, containing a gamma-butyrolactone in its structure, is an autoregulatory factor or a 'microbial hormone' controlling secondary metabolism and cellular differentiation in Streptomyces griseus. A-factor exerts its regulatory role by binding to a specific receptor protein which, in the absence of A-factor, acts as a repressor-type regulator for morphological and physiological differentiation. In the signal relay leading to streptomycin production in S. griseus, the A-factor signal is transferred from the A-factor receptor to the upstream activation sequence of a regulatory gene, strR, in the streptomycin biosynthetic gene cluster via an A-factor-dependent protein that serves as a transcription factor for strR. The StrR protein thus induced appears to activate the transcription of other streptomycin-production genes. The presence of A-factor homologues in a wide variety of Streptomyces species and distantly related bacteria implies the generality of gamma-butyrolactones as chemical cellular signalling molecules in microorganisms.

Analysis of a Het- mutation in Anabaena sp. strain PCC 7120 implicates a secondary metabolite in the regulation of heterocyst spacing

Transposon-generated mutant N10 of Anabaena sp. strain PCC 7120 has a Het- phenotype (A. Ernst, T. Black, Y. Cai, J.-M. Panoff, D. N. Tiwari, and C. P. Wolk, J. Bacteriol. 174:6025-6032, 1992). Reconstruction of the transposon mutation reproduced a Het- phenotype, but reconstructions with other insertions at the position of the transposon produced strains that form multiple contiguous heterocysts. Sequence analysis around the site of insertion of the transposon showed that the insertion lies within the 5' end of an 861-bp open reading frame (ORF) (hetN). The product of translation of hetN (HetN) shows extensive similarity to NAD(P)H-dependent oxidoreductases that are involved in biosyntheses of fatty acids, poly-beta-hydroxybutyrate, nod factor, and polyketides. A second, 1,518-bp ORF (hetM) that ends 556 bp 5' from the start of hetN appears to encode a protein that has at least two functional domains: its amino terminus is similar to an acyl carrier protein, while its central portion is similar to domains of proteins that perform reductive reactions. A third, 711-bp ORF (hetI) encoded on the opposite strand ends 42 bp away from the 3' end of hetN. The protein encoded by hetI, HetI, is similar to Sfp from Bacillus subtilis and EntD from Escherichia coli, proteins that are required for the biosynthesis or export of cyclic peptides. Clones from a lambda-EMBL3 library that contain the wild-type DNA for hetN do not complement the hetN::Tn5-1063 mutation in N10. The presence of hetN, as the only ORF, on a replicating plasmid suppresses heterocyst formation in wild-type cells, whereas the additional presence of hetI alleviates this effect.

Drug-metabolizing enzymes in ligand-modulated transcription

Genes encoding many of the so-called drug-metabolizing enzymes (DMEs) are present in both prokaryotes and eukaryotes, suggesting that these genes arose on this planet more than 3.5 billion years ago--long before animal-plant divergence (estimated to be about 1.2 billion years ago) and long before the use and commercial development of drugs. What, therefore, are the real functions of DMEs? Several years ago I proposed that DMEs are upstream in the regulatory cascade of numerous signal transduction pathways, i.e. necessary for maintaining physiologically "safe", or "acceptable", steady-state levels of all small non-protein endogenous ligands (M(r) = 250 +/- 200) in each cell. Innumerable foreign chemicals and drugs mimic these small endogenous ligands, thus binding to a particular receptor and acting either as an agonist or antagonist in activating or inhibiting genes effecting growth, differentiation, apoptosis, homeostasis and neuroendocrine functions. Discussed in this review are additional examples consistent with this theory and not described in previous reviews, including: (i) insect-plant symbiosis; (ii) "cross-talk" amongst genes in the aromatic hydrocarbon-responsive [Ah] battery; (iii) signal transduction pathways involving the arachidonic acid cascade; and (iv) the explanation in carcinogen-screening studies as to why a maximum, or half maximum, tolerated dose (MTD, MTD50) of many test compounds might cause cell division and tumorigenesis in experimental animals.

A-factor and streptomycin biosynthesis in Streptomyces griseus

Accumulating data have shown that the metabolites with a gamma-butyrolactone ring functions as an autoregulatory factor or a microbial hormone for the expression of various phenotypes not only in a variety of Streptomyces spp. but also in the distantly related bacteria. A-factor, as a representative of this type of autoregulators, triggers streptomycin biosynthesis and cellular differentiation in Streptomyces griseus. A model for the A-factor regulatory cascade on the basis of recent work is as follows. At an early step in the A-factor regulatory relay, the positive A-factor signal is first received by an A-factor receptor protein that is comparable in every aspect to eukaryotic hormone receptors, and then, via one or more regulatory steps, transmitted to an A-factor-responsive protein that binds to the upstream activation sequence of the strR gene, a regulatory gene in the streptomycin biosynthetic gene cluster. The StrR protein thus induced appears to activate the other streptomycin biosynthetic genes. This review summarizes the characteristics of A-factor as a microbial hormone and the A-factor regulatory relay leading to streptomycin production.

Pathway engineering in secondary metabolite-producing actinomycetes

Actinomycetes represent the microbial group richest in production of variable secondary metabolites. These mostly bioactive molecules are the end products of complex multistep biosynthetic pathways. Recent progress in the molecular genetics and biochemistry of the biosynthetic capacities of actinomycetes enables first attempts to redesign these pathways in a directed fashion. However, in contrast to several examples of designed biochemical improvement of primary metabolic processes in microorganisms, none of the products or strains derived from pathway engineering in actinomycetes discussed herein have reached pilot or production scale. The main reasons for this slow progress are the complicated pathways themselves, their complex regulation during the actinomycete cell cycle, and their uniqueness, as most pathways and products are specific for a strain rather than for a given species or larger taxonomic group. However, the modular use of a minimum of very similar enzymes and their conversion of similar intermediates to form the building blocks for the production of a maximum of divergent end products gives hope for the future application of these genetic models for the redesign of complex pathways for modified or new natural products. Several strategies that can be followed to reach this aim are discussed, mainly for the variable 6-deoxyhexose metabolism as an ubiquitously applicable example.

A Bacillus subtilis large ORF coding for a polypeptide highly similar to polyketide synthases

The nucleotide (nt) sequence of 13.6 kb of the outG locus of Bacillus subtilis, which maps at approximately 155 degrees between the genetic markers nrdA and polC, was determined. One putative coding sequence was identified corresponding to a large polypeptide of 4427 amino acids (aa). Structural organization at the nt and aa sequence level and extensive similarities of the deduced product, especially to EryA, suggest that the locus is potentially responsible for the synthesis of a polyketide molecule. The locus has been renamed pksX. Comparison of the deduced product with known fatty acid and polyketide synthases (PKS) suggested the presence of beta-ketosynthase, dehydratase, beta-ketoreductase and acyl-carrier protein domains. Preliminary data obtained with deletion mutants indicate that pksX is not an essential gene.

Expression of Pseudomonas aeruginosa virulence genes requires cell-to-cell communication

Pseudomonas aeruginosa is an opportunistic human pathogen that causes a variety of infections in immunocompromised hosts and individuals with cystic fibrosis. Expression of elastase, one of the virulence factors produced by this organism, requires the transcriptional activator LasR. Experiments with gene fusions show that gene lasl is essential for high expression of elastase. The lasl gene is involved in the synthesis of a diffusible molecule termed Pseudomonas autoinducer (PAI). PAI provides P. aeruginosa with a means of cell-to-cell communication that is required for the expression of virulence genes and may provide a target for therapeutic approaches.

Multiple extracellular signals govern the production of a morphogenetic protein involved in aerial mycelium formation by Streptomyces coelicolor

The formation of an aerial mycelium by the filamentous bacterium Streptomyces coelicolor is determined in part by a small morphogenetic protein called SapB. A collection of representative bald (bld) mutants, which are blocked in aerial mycelium formation, are all defective in the production of this protein and regain the capacity to undergo morphological differentiation when SapB is supplied exogenously. We now report that most of the bld mutants are rescued for SapB production and aerial mycelium formation when grown near certain other bld mutants. Extracellular complementation experiments of this kind indicate that morphological differentiation is governed by a hierarchical cascade of at least four kinds of intercellular signals. At least one such signal is present in conditioned medium. It is resistant to boiling and protease treatment, and it remains effective even when diluted up to eightfold in fresh medium.

Activity of the AIB factor observed in prokaryotic and eukaryotic microorganisms

Streptomyces cinnamonensis produces a new substance named AIB (for anti-isobutyrate) factor which, on a solid medium, efficiently counteracts toxic concentrations not only of isobutyrate but also of other salts of short-chain monocarboxylic acids. In the present study we demonstrate that the AIB factor activity is widely spread because this effect was positively detected in 25 of 31 randomly chosen microorganisms (streptomycetes, ascomycetes, zygomycetes and basidiomycetes). The AIB factor produced by the tested microorganisms on an agar media allows for germination, growth, and sporulation of the testing Streptomyces coelicolor on an agar medium containing 20 mmol/L acetate, propionate, butyrate, isobutyrate, valerate, isovalerate, and 2-methylbutyrate. The activity of the AIB factor from different sources towards these substances differs.